In a continuously variable transmission (hereafter, CVT), a pair of power rollers is gripped between an input disk and an output disk that face each other. The power rollers transmit a torque from the input disk to the output disk by friction. The power rollers are supported by trunnions.
When the trunnions are displaced in a direction of the respective trunnion axes, contact positions of the power rollers and the disks change and a direction of a force exerted by the disks on the power rollers vary. Due to this variation of force, the power rollers rotate together with the trunnions, and as a result, the contact radius of one of the input disk and the output disk increases, while the contact radius of the other disk decreases. The variation of these contact radii causes a variation of a ratio of rotation speeds of the input disk and output disk, i.e., a speed ratio. Thus, the speed ratio of the transmission can be made to vary continuously by displacing the trunnions in the trunion axis direction. The gyration angle about the trunnion axis is referred to as the gyration angle of the power roller, and corresponds directly to the speed ratio of the CVT.
When the power rollers are gripped between the input disk and the output disk, the input disk and the output disk respectively deform in an overturn direction. In order for the power rollers to follow the deformation in this overturn direction and maintain contact with both disks, they must follow the deformation of the overturn direction and must displace in the direction perpendicular to the trunnion axis and a power roller rotation axis.
In this regard, JP-A-2001-165265 published by the Japanese Patent Office in 2001, discloses power rollers free to slide in the direction perpendicular to the trunnion axis via a roller bearing unit comprising plural needle rollers and a cage which houses the plural needle rollers. The bearings slide on inclined portions of a trunnion. Projections are respectively provided at ends of the power roller cavity of the trunnion, and depressions into which the projections fit are respectively formed on each side of the cage. By providing the projections, the slide amount of the cage relative to the trunnion is limited to a gap between the cage and the projections in neutral position.
However, in the construction disclosed in JP-A-2001-165265, the roller bearing unit can be displaced in any direction of the power roller cavity, so rigidity of the inclined portions is lacking. If thrust force overdrives the trunnion, the trunnion deforms in a direction of the thrust force.
In addition, if the trunnion undergoes a large deformation, a relative position between the power roller and the disks is shifted. This causes a variation of a ratio of rotation speeds of the input disk and output disk, which is not what is intended.